The present invention relates to hydrokinetic coupling apparatus, especially for motor vehicles, such as is described for example in the document WO-A-94/07058.
In that document, the apparatus includes a generally transversely oriented wall which is arranged to be coupled in rotation to a driving shaft, and which carries, fixed thereto, a central guide ring.
A piston is mounted for axial movement sealingly along the guide ring, and defines, with the transverse wall and with the guide ring, a variable volume chamber which is bounded on the outside by a disc, together with friction liners which are adapted to be gripped, respectively, between the piston and the disc and between the disc and the transverse wall.
Each friction liner is fixed to one of the elements consisting of the disc, the piston and transverse wall between which it is adapted to be gripped.
It has previously been proposed, in the document FR-A-2 634 849, to couple the piston in rotation to the said axially fixed transverse wall, with axial mobility being obtained by means of tangentially oriented tongues which are fixed to a driving member disposed in the variable volume chamber.
In practice, this driving member is in the form of a disc which is fixed by a splined coupling to the guide ring carried centrally by, and fixed to, the said transverse wall.
As a result, the fitting of the guide ring on the transverse wall is not as easy as might be desired, because the said guide ring is equipped in advance with the disc carrying the tangential tongues coupled to the piston.
In addition, the solution is neither simple nor inexpensive, because of the splined mounting of the disc on the guide ring.
In addition, the feed to the variable volume chamber has to be obtained with the aid of channels which are formed in a known way in the said ring, and the said channels have to be arranged in such a way as to have regard to the presence of the disc, the nature of this arrangement being such as to increase the axial distance between the piston and the transverse wall.
An object of the present invention is to reduce these disadvantages in a simple and inexpensive way, while continuing to benefit from easy sliding of the piston along the guide ring and from the provision of a sub-assembly consisting of the driving member, the tangential tongues and the piston.